An example will be given of one type of transceiver pair to illustrate a conventional technique for adjusting transmit power.
In battery operated RF transceivers, the bulk of the battery power is used for transmitting. The separation between a pair of transceivers communicating with each other may change if the transceivers are in mobile or transportable devices. Further, different operating environments have different noise levels and attenuate signal power differently. In most situations, the maximum transmit power level is more than is needed for reliable digital communications. Hence, for those situations in which maximum transmit power is not needed, battery power is wasted.
One known way to optimize transmit power for a pair of communicating transceivers is as follows. The receiver generates a receive strength signal indication (RSSI) signal based on the power of the received signal. The RSSI level is transmitted back to the original transmitter. The original transmitter uses a look-up table to identify a certain transmit power level associated with the RSSI signal which was predetermined to be the optimal transmit power given that RSSI level. For example, if the RSSI signal is very high, the look-up table will identify a lower transmit power for the transmitter since the transmitter can transmit at a lower power while still ensuring reliable communication. Such a routine is performed on a periodic basis to adjust the transmit power, and such overhead uses up bandwidth.
Such a routine typically requires a microprocessor to process the data, where the microprocessor adds considerable cost to the transceiver chip.
Error correction is another function performed by many transceivers. Such error correction is treated separately from optimizing the transmit power. Error correction typically requires complex circuitry and processing. Further, error correction is part of overhead which uses up bandwidth.